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diesel electric propulsion systems

Old 10-17-2016, 11:55 AM
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Default diesel electric propulsion systems

I was thinking about the thread with the guy complaining about the only options in the high hp low weight size for large Sport-fish Yacht's being MAN and MTU. Why haven't the builders opted for diesel electric propulsion systems?

"The benefits of diesel electric drive begin with the design freedom the system affords the yacht's designer. The engine can be installed wherever appropriate to achieve optimum use of space for the accommodation. Noise and vibration are more easily suppressed than in a conventional direct engine-to-propeller drive. Turning the props with electric motors enhances slow-speed maneuverability by providing unrestricted minimum prop speeds with 100 percent torque available to provide immediate power response at all times. Prop synchronization is automatic and extremely precise. When under way all of the electrical power required by the vessel can be supplied from the diesel electric propulsion system, eliminating the need to run a genset. A diesel electric power system can drive multiple propellers from a single engine or use multiple engines to power one or more props. In a twin-engine/twin-prop system, one engine can power both props when operating within the speed limits imposed in many areas. Electrical power from the vessel's genset can be used to propel the boat, providing a built-in backup-especially valuable for yachts with single-engine installations. Conversely, the propulsion system can serve as a backup for the yacht's gensets."

Food for thought...
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Old 10-17-2016, 04:10 PM
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I'll bump this up before it falls off the second page, I agree with everything written except diesel electrics ability to compete in the high horsepower low weight arena, that's a ways off.
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Old 10-17-2016, 04:14 PM
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Maybe one large diesel engine can power two electric motors to propel a boat?
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Old 10-17-2016, 04:17 PM
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all correct. i see cost complexity and speed being the downside
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Old 10-17-2016, 06:58 PM
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Default I want one

I think I would really like it for all the reasons you mention, but I bet it would cost double the price of a normal marine engine and a generator.
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Old 10-17-2016, 07:10 PM
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Lots of positives, as discussed.

A few big negatives: Cost. Weight. Conversion losses.

Works well on cruise ships. Not ready for go-fast pleasure boats.
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Old 10-17-2016, 08:31 PM
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Originally Posted by Corndog38 View Post
Lots of positives, as discussed.

A few big negatives: Cost. Weight. Conversion losses.

Works well on cruise ships. Not ready for go-fast pleasure boats.

Cruise ships, tugboats, and locomotives are enjoying huge successes. Commercial fishing boats that spend a lot of time at low speeds are a natural candidate as well as some cruisers. The technology is moving quickly with a lot of new motors and control systems being developed but it still seems like something that I can't put my finger on is holding the technology back ( Possibly the quality and availability of reliable generators ). Some battery capacity would benefit most of these applications as well as multiple generation plants to optimize energy production in relationship to the energy needed.
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Old 10-18-2016, 04:47 AM
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"Calling Elon Musk", "Calling Elon Musk"
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Old 10-18-2016, 04:59 AM
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Diesel electric propulsion has been common in heavy mining equipment for decades. However the last ten years has seen a big increase due to the advent of AC technology.

In that application the benefits are pretty obvious, as the electric drive train replaces a number of heavy mechanical components. I'd think in smallish vessels with shaft drives the benefits are not readily obvious.
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Old 10-18-2016, 05:04 AM
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I think the main drawback on smaller boats would be almost double the weight of the drive system. Big electric motors are not light.
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Old 10-18-2016, 05:07 AM
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Sounds cost prohibitive for smaller aps

Also diesel motors pretty simple to maintain operate and repair. DME will prob require an engineer on board. Factor that into cost as well
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Old 10-18-2016, 05:13 AM
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Locomotives are primarily diesel electric . Great for high forces needed at low speeds. Used to be DC but now AC driven. Very controllable and very sensitive circuitry detects "Wheel Slip" and can vary power very quickly to keep tractive effort.

Weight would be a major factor.
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Old 10-18-2016, 05:16 AM
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Originally Posted by Corndog38 View Post
Lots of positives, as discussed.

A few big negatives: Cost. Weight. Conversion losses.

Works well on cruise ships. Not ready for go-fast pleasure boats.
From a ship engineer you are correct also very complex and a real head scratcher when it doesn't work as designed...
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Old 10-18-2016, 05:41 AM
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I would think they would be perfect in displacement boats that only run at hull speed.
A trawler with 2 electric engines and one decent sized genset would be great.

The HP needed to get a cruiser up on plane would be pretty high and a pretty big genset would be needed to run it.

Last edited by chuck34; 10-18-2016 at 06:34 AM.
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Old 10-18-2016, 06:35 AM
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Apparently Glacier Bay had/has diesel-electric system.

http://www.powerandmotoryacht.com/en...et-alternative
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Old 10-18-2016, 06:54 AM
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There was an article in Passage Maker magazine some years ago about the conversion of a trawler to diesel electric, with one big diesel generator and 2 electric motors. What really got my attention was the size of the electric motors, they were huge, and also they needed a raw water system for cooling them. I do not remember the performance data, but in my uneducated view the complexity of the system plus the cost did not justify the installation.
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Old 10-18-2016, 06:57 AM
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I rented a 42' diesel electric powered sailing catamaran several years ago. The electric motors by themselves where almost as big as the traditional 35HP diesels. The generator was enormous-and heavy. With only 26kw available, the boat was substantially underpowered. Under sail, the boat was a complete pig due to the extra weight of the drive gear. When motorsailing, the only way you could get this thing to move, it still burned 3-4gph which is twice what the same boat burns with traditional propulsion. The oversized main generator also burned a ton of fuel at anchor just to run the AC.

IMO, high cost, complexity and poor performance made the whole design a complete fail.

On a 42' trawler, you would need 4x the power and a second generator for use at anchor.
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Old 10-18-2016, 07:13 AM
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Nordhaven did it and ended up quietly buying back boats and fitting traditional drive setups in them.
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Old 10-18-2016, 07:25 AM
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consider this. You have to have a big generator on the end of the diesel engine(s) to produce the electricity, then you have to have 2 big electric motors to drive the propellers. Im sure there are other systems required as well. You have also lost energy by converting that mechaincal force into electricity and then back into force again. Also you have added too much weight and taken up too much space in a typical sportfishing boat
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Old 10-18-2016, 07:33 AM
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I could maybe see an advantage if used in parallel with a traditional drive system in something like a large sporty. For instance ours has 2 gensets and 2 mains. 1 genset will run the entire boat, the 2nd is a backup. If two electric motors could be powered by the extra 25kw genset and push the boat at 10 knots it might be worth doing instead of running both mains when moving the boat longs distances at displacement speed.

There likely isn't much fuel savings there because at just above idle the mains are not burning a ton of fuel. There are more tangible savings for keeping the hours off the much more expensive main engines if speed is not required. Could also be handy around the dock or in long no wake areas where the boat really moves too fast at traditional idle.

Upfront costs as well as complexity likely still makes this impractical even given the best case scenario where the boat already has enough generator power to make it work.
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